CLOSURE OF HLW TANKS FORMULATION FOR A COOLING COIL GROUT

Abstract

The Tank Closure and Technology Development Groups are developing a strategy for closing the High Level Waste (HLW) tanks at the Savannah River Site (SRS). Two Type IV tanks, 17 and 20 in the F-Area Tank Farm, have been successfully filled with grout. Type IV tanks at SRS do not contain cooling coils; on the other hand, the majority of the tanks (Type I, II, III and IIIA) do contain cooling coils. The current concept for closing tanks equipped with cooling coils is to pump grout into the cooling coils to prevent pathways for infiltrating water after tank closure. This task addresses the use of grout to fill intact cooling coils present in most of the remaining HLW tanks on Site. The overall task was divided into two phases. Phase 1 focused on the development of a grout formulation (mix design) suitable for filling the HLW tank cooling coils. Phase 2 will be a large-scale demonstration of the filling of simulated cooling coils under field conditions using the cooling coil grout mix design recommended from Phase 1. This report summarizes the results of Phase 1, the development of the cooling coil grout formulation. A grout formulation is recommended for themore » full scale testing at Clemson Environmental Technology Laboratory (CETL) that is composed by mass of 90% Masterflow (MF) 816 (a commercially available cable grout) and 10% blast furnace slag, with a water to cementitious material (MF 816 + slag) ratio of 0.33. This formulation produces a grout that meets the fresh and cured grout requirements detailed in the Task Technical Plan (2). The grout showed excellent workability under continuous mixing with minimal change in rheology. An alternative formulation using 90% MF 1341 and 10% blast furnace slag with a water to cementitious material ratio of 0.29 is also acceptable and generates less heat per gram than the MF 816 plus slag mix. However this MF 1341 mix has a higher plastic viscosity than the MF 816 mix due to the presence of sand in the MF 1341 cable grout and a lower water to solids ratio. Nevertheless, the higher viscosity grout may still meet the requirements for the cooling coil grout under certain pumping conditions or alternatively, the mix may be made more fluid by a short period of high shear mixing during production. The mixes have not been optimized for large scale production. It may be possible, for example, to adjust the water to cementitious materials ratio to provide improved performance of these mixes based on the results and conclusions of the large scale testing at CETL. Recommendations from this task include incorporation of a backup mixing/pumping system that is either integrated into the system or is available for immediate use in case of a pump or mixer failure of the primary system. A second recommendation is to conduct a laboratory scale investigation to determine the impact of operational variation on the properties of the grout. This effort would be initiated after feedback is received from the large scale testing at CETL. The purpose of this proposed variability testing is to better understand the limits of the operational variations (such as temperature and mixing time), and to identify possible approaches for remediation to ensure that the grout produced will flow effectively in the coils while still meeting the performance requirements.« less